1. Field of the Invention
The present invention relates to a support for a lithographic printing plate and a presensitized plate.
1) More particularly, the present invention relates to the support for the lithographic printing plate and to a presensitized plate using the support for the lithographic printing plate where an ink spreading hardly occurs in a halftone dot area and left-plate scum resistance under a low humidity environment is excellent when the lithographic printing plate is manufactured, since water-receptivity is excellent. Further the present invention relates to a presensitized plate where a dot residual layer hardly occurs and to the support for the lithographic printing plate used in the presensitized plate besides the aforementioned characteristics.
2) More particularly the present invention relates to the support for the lithographic printing plate and to the presensitized plate from which the lithographic printing plate can be prepared with the effects that scum resistance is excellent, specially, a scum (scumming) on non-image areas hardly occurs even if the quantity of a fountain solution is reduced, an adhesion between an image recording layer and the support on image areas is strong, press life is excellent, and an inadequate inking on a solid area (solid image area) hardly occurs. Further the present invention relates to the support for the lithographic printing plate and to the presensitized plate from which the lithographic printing plate can be manufactured with the effects that the property that press life does not deteriorate, although the printing plate is wiped with a plate cleaner (cleaner press life) besides the aforementioned characteristics. Moreover the present invention relates to the support for the lithographic printing plate and to the presensitized plate from which the lithographic printing plate can be manufactured with the effects that a locally dotted stain (dot residual layer) hardly occurs, specially, the generation prevention effect of the dot residual layer is excellent when the image recording layer of a laser directly-drawn type is provided besides the aforementioned characteristics.
3) More particularly, the present invention relates to the support for the lithographic printing plate and to the presensitized plate using the support for the lithographic printing plate where an adhesion between a photosensitive layer and the support is excellent, especially, UV ink resistance is excellent on image areas and a scum hardly occurs on non-image areas.
2. Description of the Related Art
Lithography is a printing system capitalizing on the property that water and oil do not mix basically, and an area which receives water and repels an oily ink (hereinafter, this area is called “a non-image area”) and an area which repels water and receives the oily ink (hereinafter, this area is called “an image area”) are formed on the printing plate of a lithographic printing plate used for the lithography.
Since an aluminum support for the lithographic printing plate used for the lithographic printing plate (hereinafter, merely called “a support for the lithographic printing plate”) is used so as to allow the surface of the support to function as a non-image area, various contradictory performances such as excellent water wettability, water receptivity, and an excellent adhesion between the support for the lithographic printing plate and an image recording layer provided thereon are required.
If the water wettability of the support for the lithographic plate is too low, ink is likely to be attached to the non-image areas at the time of printing, causing a blanket cylinder to be scummed and thereby causing so-called scumming to be generated. In addition, if the water receptivity of the support plate is too low, clogging in the shadow area is generated if the flow of a fountain solution is not increased at the time of printing. Thus, a so-called water allowance is narrowed.
1) On the one hand, if deep recesses are existent on the surface of the support for the lithographic printing plate on which a graining is performed, a development may be suppressed according to shapes on the surface since the image recording layer on that portion is thickened. Then, as a result of suppressed development, the image recording layer is left in the deep recesses, local residual layers (hereinafter, also called “dot residual layers”) are generated, thus causing a problem that the non-image areas are scummed at the time of printing. For example, in a presensitized plate where a so-called thermal type image recording layer is provided in which the solubility to an alkali developer varies with heat generated by photo-thermal conversion, an image formation reaction is insufficient at the bottom of the recesses, thereby the dot residual layers are generated.
Such the dot residual layers are likely to take place if the conditions of exposure and development are tight. For example, in a presensitized plate provided with the thermal type image recording layer, such a case as that the exposure quantity of a laser is lowered by shortening exposure time to increase productivity, by lowering a laser light energy to extend the service life of the laser and the like. In addition, such a case also as that a development is performed by using a low-sensitivity developer and the like, since an image recording layer where non-image portions likely tend to take place on an area which is basically to be an image area is used to a highly-sensitive and highly active developer.
2) On the other hand, it is preferable that the asperities on the surface of a non-image area are smooth so as not to allow unnecessary ink to be attached in order to keep scum resistance. However, if the asperities of the surface are smoothened, the adhesion between the image recording layer and the support for the lithographic printing plate deteriorates, thereby press life deteriorates. Namely, scum resistance and press life are in the relation of trade-off.
3) In addition, in another case, if the water wettability of the support for the lithographic printing plate is too low, ink is likely to be attached to the non-image areas at the time of printing, thereby causing ink scum, particularly the gap to be scummed. In addition, if the water allowance is narrow, spreading of halftone dots may take place, depending upon kinds of ink.
Although a gap scum belongs to an ink scum evaluated by the sheets needed for ink repelling, it is another scum different from a scum which is left in the vicinity of the image areas at the initial stage of printing. The non-image area between the vicinity of an area of PS plate which is fixed on the plate cylinder (lower gripper area) and the image area on the side of PS plate wound around the plate cylinder contacts with the blanket cylinder is called a gap. When printing is started, ink is likely to be attached to this gap which is scummed with the ink. This is called a gap scum. Since this scum gradually disappears as water and ink are supplied in a printing process, usually, it is simultaneously evaluated as sheets needed for ink repelling.
The gap scum is observed as the scum of the non-image areas between the image areas and the gripper areas under a place where the gripper areas are provided at the upper and the lower positions and the image areas are provide at the center when PS plate is removed from the plate cylinder, opened and extended. Since the gap scum is likely to take place, if greater fine irregular structures (asperities) are existent on the surface of the support for the lithographic printing plate, it is contrary to a technological requirement for increasing an adhesion between the support for the lithographic printing plate and the image areas.
In order to solve the aforementioned problems to obtain the support for the lithographic printing plate with a good performance, it is general to give asperities by performing graining (graining treatment) on the surface of an aluminum plate. For the asperities, various shapes are proposed as shown below. JP 8-300844 A describes a triple structure which is formed of large, medium and small undulations in which the aperture diameters of a grained structure with medium and small undulations are defined. JP 11-99758 A and JP 11-208138 A describe the definition of the diameter of a grained structure with small undulation in the double structure of a grained structure with large and small undulations. JP 11-167207 A describes a technology which gives finer protrusions besides the double, which is large and small, recesses (pits). JP Patent No. 2023476 (Specification) describes a double structure where the diameter of an aperture is defined. JP 8-300843 A describes a double structure where a factor a30 which shows the smoothness of a surface is defined. JP 10-35133 A describes a structure where the ratio of the diameters of pits superimposed in a plurality of electrochemical graining treatments (hereinafter, also referred to as “electrolytic graining treatments”) is defined.
Used for this graining are mechanical graining methods such as ball graining, brush graining, wire graining and blast graining, electrolytic graining method where electrolytic etching is performed on an aluminum plate in an electrolyte containing hydrochloric acid and/or nitric acid, and U.S. Pat. No. 4,476,006 describes a complex graining method combining mechanical graining method with electrolytic graining method.
However, various kinds of inks are now used depending upon applications at printing sites and these inks each has the different physical properties of the solutions.
1-1) In an aforementioned conventional art, since water receptivity is not sufficient, the art has the problems that there occurs a trouble that a phenomenon that the ink in the image areas is apt to move to the non-image areas if the fountain solution is reduced during printing (hereinafter, called “ink spreading in the halftone dot areas” and a difficulty of the generation of this phenomenon is called “difficulty of spreading”) is likely to take place and left-plate scum resistance is also poor, particularly in the halftone dot area of high image area ratio among the image areas (hereinafter, called “shadow area”), depending upon kinds of inks and fountain solutions. This ink spreading in the halftone dot areas is highly likely to be affected by the physical properties of the ink and the fountain solution.
Therefore, the present invention is directed to solve this problem and provide the support for the lithographic printing plate and the presensitized plate using the support for the lithographic printing plate where the ink spreading in the halftone dot areas hardly occurs and left-plate scum resistance is excellent, regardless of the kind of ink or fountain solution when a lithographic printing plate is manufactured.
1-2) In addition, it is effective to increase the surface roughness to improve water receptivity. However, if the surface roughness is increased, locally deep recesses are likely to be generated. The deep recesses cause a defective exposure and development, thereby dot residual layers are likely to be generated.
Therefore, the present invention is directed to provide the support for the lithographic printing plate and the presensitized plate using the same where the ink spreading in the halftone dot areas hardly occurs, left-plate scum resistance is excellent and further, dot residual layers are not generated irrespective of the kind of an ink or a fountain solution when the lithographic printing plate is manufactured.
2-1) In addition, if a recycled paper on the surface of which a coating component is coated to increase the whiteness degree (hereinafter, called “a coated recycled paper”) is used as a material to be printed, an inadequate inking may take place in a solid area, and this is problematic.
However, the support for the lithographic printing plate where water wettability, water receptivity, scrum resistance, adhesion with the image recording layer are excellent, and an inadequate inking in the solid areas does not occur if printing is performed by using a coated recycled paper has not been realized yet.
Therefore, the present invention is directed to provide the presensitized plate and the support for the lithographic printing plate used therefore where press life and scum resistance are excellent, and an inadequate inking in the solid areas hardly occur if the coated recycled paper is used when the lithographic printing plate is manufactured.
3-1) The aforementioned conventional arts have further problems, depending upon the kinds of inks. A UV-curing ink has been recently used as an image recording layer. The UV ink chiefly includes a monomer and a pigment and is hardened by irradiating the monomer with ultraviolet rays to perform coloring. Particularly, since the UV-curing ink per se derived from the monomer or a treatment chemical used for printing by employing the UV-curing ink, particularly, a mineral spirit, a plate cleaner or the like must be stronger than the processing chemicals, there has occurred a problem that an adhesion is further damaged if a solution layer derived from these chemicals is formed between the image areas and the support for the lithographic printing plate. For that reason, the surface shape of the support for the lithographic printing plate has been further required to be investigated.
3-2) In addition, there was a disadvantage that an ink is likely to be attached to the non-image areas in the shadow area where a fountain solution is reduced, namely in the halftone dot areas (hereinafter, this phenomenon is called “ink spreading” and a degree of difficulty that this phenomenon hardly occurs is called “difficulty of spreading”, depending upon the kinds of inks and in addition, there was also a problem that left-plate scum resistance was poor.
Therefore, the present invention is directed to solve this problem and provide the presensitized plate and the support for the lithographic printing plate used for the same where the adhesion between the photosensitive layer and the support for the lithographic printing plate is excellent in the image areas, particularly UV-curing ink resistance is excellent, and ink scum and gap scum hardly occur in the non-image areas.
3-3) The present invention is preferably directed to provide the support for the lithographic printing plate and a presensitized plate using the same having the optimum surface shape capable of preventing the attachment of ink to the non-image areas in the halftone dot areas (halftone dot spreading) even if a fountain solution is reduced, irrespective of the kind of an ink when a lithographic printing plate is manufactured.